1. Field of the Invention
This invention relates to telecommunications networks and, more particularly, to a method for reducing information error rates and increasing throughput of communication channels within telecommunication networks.
2. Description of the Related Art
The use of communication networks such as telephony networks and data communication networks (e.g., the Internet) by the general public to convey information has increased significantly in the past several years. The information is represented by analog and/or digital communication signals. A telephony network provides traditional telephony services (e.g., voice communications, facsimile communications, analog data) over such media as twisted metallic wire pairs (e.g., tip/ring pairs), coaxial cables, fiber optic cables, air, free space, and other media. The Public Switched Telephone Network (PSTN) is an established telephony network which is accessible to the general public. A data communication network is a network in which information signals are conveyed throughout the network in digital form. Examples of a data communication network include the public Internet and computer communication networks (e.g., corporate communication networks, educational communication networks, governmental communication networks).
Often, users of telephony networks, computer communication networks, and other communication networks gain access to such networks via local access networks such as a Digital Loop Carrier (DLC) system. An exemplary DLC system is shown in FIG. 1. DLC 10 comprises Remote Terminal (RT) 28 connected to Local Digital Switch (LDS) 20 via communication link 26. Communication signals are exchanged between LDS 20 and communication link 26 via interface 24. LDS 20 is connected to PSTN 12 and Public Internet 14 via communication links 18 and 16, respectively. Remote Terminal 28 is connected to user 1 (34) via communication link 30 and to user 2 (36) via communication link 32. Users 1 and 2 thus have access to PSTN 12, Public Internet 14, and to each other. For the sake of clarity only two users are shown in FIG. 1. In practice, DLC systems connect hundreds or even thousands of users. Moreover, an actual DLC system, such as the one shown in FIG. 1, may provide access to a variety of communication networks in addition to the ones shown.
Communication links 30 and 32 are currently implemented with metallic wires (i.e., tip/ring pairs) through which analog communication signals (e.g., voice, facsimile) are conveyed between the users (30, 32) and Remote Terminal 28. Communication links 30 and 32, when implemented as metallic tip/ring pairs, are part of the well-known Plain Old Telephone Service (POTS) telephony system and such links are commonly referred to as POTS lines. POTS lines typically are able to convey analog communication signals within a limited bandwidth spanning the frequency range of 0-4 KHz, commonly referred to as Voice Frequencies (VF). The VF range is typically further band limited to a frequency range of 200-3400 Hz due to additional analog filtering by DLC 10 equipment.
Users who wish to communicate with data communication networks, such as the Public Internet, typically use modems to transmit and receive analog data signals over the POTS lines. The analog signals from communication links 30 and 32 are converted to digital signals by RT 28 and are conveyed over communication link 26. The digital signals are processed in accordance with a protocol being followed by DLC 10 and are transferred to LDS 20 which transmits such digital signals to either PSTN 12 or Public Internet 14 via communication links 18 or 16, respectively. A protocol is a set of rules and standards that govern the operation of the various equipment of a communication network such as a local access network so as to control, monitor, and/or manage communications between users of the same or different networks and also between equipment of the same or different networks. Part of the protocol information is referred to as signaling information which is used to initiate communication between users, monitor the channel through which information is being conveyed during user communications, and terminate communications between users. The signaling information is often generated by the various communication network equipment (e.g., RT 28, LDS 20).
Before users of the same or different networks can communicate with each other, the communication is established in accordance with the protocol. A communication is established when the system has allocated appropriate network resources (e.g., a communication channel) and has followed certain procedural steps defined by the protocol, to allow users to convey communication signals to each other within a communication network or different networks. The communication signals conveyed between users is referred to as user information. Examples of protocols used by local access networks (particularly in North America) include the well-known TR-303 Hybrid Signaling protocol and the TR-008 protocol.
Still referring to FIG. 1, LDS 20 also receives user information from either PSTN 12 or Public Internet 14 and transmits such information to RT 28 which converts the information to the proper analog signal for propagation through communication links 30 or 32. The signaling information is extracted by RT 28 and the remaining user information is relayed to the users. It should also be noted that communication links 30 and 32 need not be analog POTS lines, but can be other communication links through which digital and/or analog communication signals are conveyed.
The user information conveyed through the various communication links of local access network 10 is packaged and structured in accordance with well-defined communication channel formats. An example of a communication channel format used in many local access networks and other communication networks is the well-known Digital Signal Zero (DS0) channel format. A DS0 channel is defined as a communication channel with an information capacity of 64 kbps (64,000 bits per second). Part of the information conveyed through the communication channels represents protocol information. Communication links can be also be formatted as per a Digital Signal One (DS1) structure. A DS1 contains 24 DS0 channels.
The digital signals conveyed between RT 28 and LDS 20 over communication link 26 are organized in a particular fashion dictated by the protocol being followed by the local access network.
Referring to FIG. 2, there is shown how digital signals are organized and conveyed over communication link 26 between LDS 20 and RT 28 as per the TR-303 Hybrid Signaling protocol. Communication link 26 is organized as a DS1. Typically, the analog signals from the users are sampled by RT 28 at a rate of 8000 samples per second. RT 28 converts each sample to an 8-bit word, which is then placed in a particular DS0 channel within the DS1 of communication link 26. In particular, the digital signals are organized as frames 38, with each frame being 125 xcexcsec long (i.e., length of one sample). Each frame 38 comprises data for 24 DS0 channels 40, where each DS0 channel contains the 8 bits of data representing a sample from a particular user, and a framing bit 43 used as an indicator for separating the frames. Thus, a DS1 can serve up to 24 separate users.
The TR-303 Hybrid Signaling protocol allows signaling information to be integrated with user information and both types of information are conveyed through the DS1. Such a technique of integrating user information with signaling information is commonly referred to as in-band signaling (or in-slot signaling). Still referring to FIG. 2, part of each user""s information, and in particular, the least significant bit 42 of each DS0 channel of every sixth frame is discarded and replaced with a signaling bit that represents signaling information for that DS0 channel. The information that replaces the discarded user information is referred to as in-band signaling information. The in-band""signaling scheme where the least significant bit of user information is purposely discarded and replaced with signaling information is referred to as robbed-bit signaling (RBS). The TR-303 Hybrid Signaling protocol uses the robbed-bit signaling scheme.
FIG. 2 discloses a particular form of RBS structured in what is commonly known as a DS1 frame format. In this particular version of RBS, the least significant bit 42 of every DS0 channel within the 6th frame, the 12th frame, the 18th frame, the 24th frame, etc., is replaced with signaling information. For purposes of clarity, only the configuration of the 6th frame is shown in FIG. 2.
As the popularity of data communication networks such as the Internet increases, there is an ever increasing need by users of local access networks to convey information to and from such networks at higher and higher speeds. At such high speeds and in view of the limited bandwidth of the POTS lines, signal degradation is often a problem. The analog data signals tend to be more susceptible to noise and are more easily distorted by bandwidth limited media such as POTS lines.
It will be readily understood that the use of the RBS scheme, or other in-band signaling schemes, in which part of the user information is sacrificed for signaling information, is another contributor to the signal degradation suffered by local access network 10 and other similar communication networks. The use of in-band signaling schemes often degrades the performance of local access networks and other communication networks, because of the increase in the information error rate (e.g., high bit error rates) and/or lowered throughput. Typically, a certain amount of errors occurs in the conveyance of user information at a particular speed for a particular amount time. For a certain time period, the ratio of the amount of errors occurring in conveyed user information to the amount of user information is defined as information error rate. The throughput is defined as the actual amount of information conveyed. Often, subscribers or the local access network equipment must reduce the speed at which information is being conveyed through the local access network in order to lower the information error rates to an acceptable level. For example, many subscribers who use 56 Kb/s, 33.6 Kb/s or even 28.8 Kb/s modems to convey information through communication channels of local access networks have to operate their modems at lower speeds because of the exacerbating effects of in-band signaling such as RBS. As a result, the throughput of these communication channels is decreased.
It is therefore, an object of the present invention to eliminate substantially the adverse effects (e.g., increased information error rate, lowered throughput) of in-band signaling schemes such as RBS during communications between users of local access networks or other communication networks.
The present invention provides for a method, which when applied to a communication network that uses in-band signaling, suspends the application of in-band signaling for at least a portion of established communication between at least two users of the communication so as to reduce information error rates associated with the established communication. The method of the present invention comprises the steps of establishing communication between at least two users in accordance with a protocol and conveying information free of in-band signaling information so as to reduce information error rates associated with the conveyed user information.
In one embodiment, the present invention is a method for conveying information in a communication network, the method comprising the steps of (a) establishing communication in accordance with a protocol; and (b) conveying user information free of in-band signaling information so as to reduce information error rates associated with the conveyed user information.
In another embodiment, the present invention is a method for conveying information in a local access network that follows a protocol which uses in-band signaling, the method comprising the steps of (a) establishing communication between at least two users in accordance with the protocol; (b) suspending in-band signaling; (c) entering a clear channel mode; (d) remaining in the clear channel mode until it is determined that conditions exist which warrant returning to in-band signaling; and (e) ending the established communication when at least one of the users terminates communication.
In yet another embodiment, the present invention is a method for conveying information in a DLC communication network that follows the TR-303 Hybrid or TR-008 Signaling protocol, the method comprising the steps of (a) establishing communication between at least two users using a DS1 frame format for the robbed-bit signaling scheme in accordance with the TR-303 Hybrid or TR-008 Signaling protocol; (b) suspending the use of robbed-bit signaling; (c) entering a clear channel mode; (d) resuming robbed-bit signaling when it has been determined that conditions exist that warrant returning to in-band signaling; and (e) ending the established communication as per the TR-303 Hybrid or TR-008 Signaling protocol when at least one of the users goes on hook.